/usr/share/X11/xkb/symbols/parens is in xkb-data 2.23.1-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 | // swap parentheses and square brackets
partial default
xkb_symbols "swap_brackets" {
replace key <AE09> { [ 9, bracketleft ] };
replace key <AE10> { [ 0, bracketright ] };
replace key <AD11> { [ parenleft, braceleft ] };
replace key <AD12> { [ parenright, braceright ] };
};
|